The present invention relates to a disk array system, particularly, to a disk array system adapted for a simple interface such as an ATA interface.
Recently, instead of FC (Fibre Channel) drives and SCSI (Small Computer System Interface) drives conventionally used, low-cost ATA (AT Attachment) drives designed for personal computers have been frequently used in disk arrays for backups/archives. The ATA drive executes an automatic reassignment for automatically assigning data of a bad sector to another sector. A retry is executed many times to succeed in accessing disks (for example, see “Hard Disk Drive Specification Deskstar 7K250”, Hitachi Ltd., 13 Aug. 2003.
On the other hand, in conventional disk arrays using the FC drives and SCSI drives, to increase their reliability, symptom of failure of the drives is monitored, and when many bad sectors occur, preventive copy is executed. The disk controller monitors the number of occurrences of the bad sectors to detect a trigger of this preventive copy.